Using the Roach Formula to Stratify Patients with Localised Prostate Cancer Treated with Intensity-modulated Radiotherapy

Objectives: The Roach formula can be used to calculate the risk of pelvic lymph node involvement in patients
with prostate cancer. This study aimed to use the Roach formula to further differentiate high-risk patients at
risk of treatment failure after intensity-modulated radiotherapy (IMRT), and to identify factors associated with
biochemical failure-free survival (bFFS).

Methods: Records of consecutive patients with biopsy-proven localised prostate cancer (T1-4 N0M0) who
underwent prostate-only IMRT between February 2006 and August 2011 were retrospectively reviewed.
Neoadjuvant and concomitant androgen deprivation therapy (ADT) was given to intermediate- and high-risk
patients, whereas adjuvant ADT was given to high-risk patients for 2 to 3 years if they could afford this self-financed
item. Patients were divided into three groups of lymph node involvement based on the Roach formula
(≤15%, >15-35%, and >35% risk) and their bFFS were compared. Factors associated with bFFS were identified
using univariate and multivariate analyses.

Results: The median follow-up duration of 144 patients was 55.8 months. According to the National Institute for
Health and Care Excellence classification, 6%, 30%, and 64% of patients were stratified as low, intermediate, and
high risk, respectively. According to the Roach formula, 35%, 28%, and 37% of patients were stratified as low,
(≤15%), intermediate (>15-35%), and high (>35%) risk of lymph node involvement, respectively. Biochemical
failure occurred in 23 patients. The median bFFS was 48.5 months. The 5-year bFFS in the three groups of ≤15%,
>15-35%, and >35% risk of lymph node involvement based on the Roach formula were 100%, 87.7%, and 75.4%,
respectively (p = 0.003). In multivariate analysis, significant factors associated with better bFFS were patient age
of >75 years, pretreatment serum prostate-specific antigen (PSA) of ≤20 ng/ml, undetectable serum PSA after
IMRT, and longer duration of adjuvant ADT.

Conclusion: The Roach formula can further differentiate patients at higher risk (>15-35% and >35%) of lymph
node involvement to receive more intensified IMRT and closer monitoring to improve their bFFS.